1. Field of the Invention
The present invention relates to a method and apparatus for simultaneously reducing various kinds of noises in an image output from an image sensor equipped to a camera, and more particularly, to a method and apparatus for simultaneously reducing a white Gaussian noise and an impulse noise in a color filter array (CFA) Bayer pattern image output from an image sensor.
2. Description of the Related Art
An image sensor attached to a camera converts light entering from an external source into an electrical signal. Image sensors are being applied to various digital image media, such as portable multimedia players (PMPs), mobile phones, etc., in addition to cameras. Recently, it has been intended to equip vehicles with such cameras in order to monitor driving environments. This application of image sensors to various digital image media devices is becoming more popular. In particular, when an image output from an image sensor is reproduced on a high-resolution display panel, noises included in the image appear. For this reason, the technology of removing noises from an image output from the image sensor is being considered as a core technology.
Representative examples of image noises include a white Gaussian noise and an impulse noise. The white Gaussian noise refers to a noise which statistically always exists in a wide frequency range in the form of being overlapped with the original signal. In order to reduce the white Gaussian noise included in an image, a color value of a particular pixel of the image is corrected by appropriately weighted-averaging the color value of the particular pixel and color values of neighboring pixels.
Meanwhile, the impulse noise refers to an instantaneous sharp noise which has completely different features from those of an original signal. In general, the impulse noise generates in an internal circuit of a device or a transmission path. In particular, in cameras, the impulse noise is generated during an image capturing process performed by an image sensor. In order to reduce the impulse noise included in an image, the median value among the color values of neighboring pixels around a current pixel of the image is used as the pixel value of the current pixel.
Recently, a huge amount of research into a unified filter for simultaneously removing the white Gaussian noise and the impulse noise has been performed. Representative examples of such research into the unified filter are as follows: “A universal noise removal algorithm with an impulse detector” (Roman GARNETT, Timothy HUEGERICH, Charles CHUI, WENJIE HE, IEEE transactions on image processing, Volume 14, Number 11, Page 1747-1754, November 2005); “An adaptive spatial filter for additive Gaussian and impulse noise reduction in video signals” (Yong HuangHui, L., Proceedings of the 2003 Joint Conference of the Fourth International Conference, 15-18 Dec. 2003, Volume 1, Page 523-526; and “Fast method for noise level estimation and integrated noise reduction” (Bosco, A. Bruna, A. Messina, G. Spampinato, G., IEEE Transactions on Consumer Electronics, Volume 51, Issue 3, Page 1028-1033, August 2005).
However, these conventional unified filters requires a complicated computing process and may lead to the blurring of fine details of the image after being applied to reduce noises in the image.